1. Field of the Invention
This invention relates to a display-integrated tablet device, and more particularly to a device in which a display and a tablet capable of carrying out coordinate input are integrated with each other.
2. Description of the Prior Art
A conventional display-integrated tablet device is generally constructed in such a manner as shown in FIG. 9. More specifically, a conventional display-integrated tablet device generally designated by reference numeral 30 in FIG. 9 includes a matrix tablet (hereinafter merely referred to as "tablet") 31 which comprises a thin film electric luminescence (EL) matrix tablet. The tablet 31 includes X-electrodes x.sub.1 to x.sub.m arranged in a column direction for carrying out horizontal scanning and Y-electrodes Y.sub.1 to Y.sub.n arranged in a row direction for carrying out vertical scanning, so that the X-electrodes and Y-electrodes cooperate with each other to form a matrix.
The X-electrodes x.sub.1 to x.sub.m each are connected to a X-scanning driver 32, which functions to apply a scan voltage to the X-electrodes x.sub.1 to x.sub.m at a predetermined timing according to control by a driver controller 34. The Y-electrodes y.sub.1 to y.sub.n are commonly connected to a Y-scan driver 33, which likewise applies a scan voltage to the Y-electrodes y.sub.1 to y.sub.m at a predetermined timing according to control by the driver controller 34.
The display-integrated tablet device 30 also includes a CPU 35 for carrying out image display scan control, as well as carrying out detection operation of an input coordinate indicated through a stylus pen 36 based on a peak detection signal at a predetermined timing as described hereinafter.
The stylus pen 36 includes a distal end or pen point for detection, which is adapted to be abutted against the tablet to carry out coordinate input according to an electrostatic capacity coupling system. Reference numeral 37 designates an amplifier for amplifying a coordinate detection signal output from the stylus pen 36 and 38 is a peak detection section for carrying out peak detection with respect to the coordinate detection signal fed from the stylus pen 36 through the amplifier 37, to thereby feed a coordinate position at which a peak of the signal is detected to the CPU 35.
Now, display operation and coordinate input operation carried out by the conventional display-integrated tablet device 30 thus constructed will be described hereinafter with reference to FIGS. 10(a) to 10(l) and FIG. 11.
FIGS. 10(a) to 10(l) each show a waveform of a timing at which scanning of each of the X-electrodes x.sub.1 to x.sub.m and Y-electrodes y.sub.1 to y.sub.n of the tablet 31 is executed by each of the X-scan driver 32 and Y-scan driver 33. As shown in FIG. 10, supposing that a period during which display for one picture plane is carried out and a period during which a pen input position is detected are defined to be a one-image-plane display period corresponding to one frame or one field period, the period is separated into a display period during which display operation is actually carried out and Y- and X-coordinate detection periods.
During the display period, the Y-scan driver 33 applies a scan voltage to the Y-electrodes y.sub.1 to y.sub.n in turn as shown in FIGS. 10(a) to 10(c), to thereby execute vertical scanning. More specifically, application of the voltage to the Y-electrodes y.sub.1 to y.sub.n is carried out by one line for every one time depending on a vertical/horizontal synchronous signal. The X-scan driver 32 applies a voltage to the X-electrodes x.sub.1 to x.sub.m within a scan period of each of the Y-electrodes y.sub.1 to y.sub.n depending on display data fed thereto from the driver controller 34 as shown in FIGS. 10(d) to 10(f). More specifically, the X-scan driver 32 applies the voltage to the X-electrodes corresponding to display cells in the Y-electrodes (horizontal lines) in turn.
Therefore, during scanning of each of the Y-electrodes, a phosphor of each of picture cells intersecting the X-electrodes having a voltage applied thereto is excited for luminescence due to formation of an electric field by the X-electrodes and Y-electrodes, resulting in display operation being carried out.
FIGS. 10(g) to 10(l) each enlargedly show a scan timing of the X-electrodes x.sub.1 to x.sub.m while enlarging a scan period of the Y electrodes y.sub.1 and Y.sub.2.
When such a display period terminates, operation for a Y-coordinate detection period takes places. An X-coordinate detection period following the Y-coordinate detection period is defined for detecting coordinate input due to abutment of the stylus pen 36 against the tablet 31.
First, during the Y-coordinate detection period, only the Y-scan driver 33 applies a detection voltage to the Y-electrodes y.sub.1 to y.sub.n in turn as shown in FIGS. 10(a) to 10(c). Therefore, when the pen point of the stylus pen 36 is kept abutted against a location on the tablet 31, electrostatic capacity coupling occurs between the Y-electrode positioned in proximity to the location and the stylus pen 36, so that a voltage is output in the form of a coordinate detection signal from the stylus pen 36.
Also, during the X-coordinate detection period, only the X-scan driver 32 applies a detection voltage to the X-electrodes x.sub.1 to x.sub.m in turn as shown in FIGS. 10(d) to 10(f) Thus, when the pen point of the stylus pen 36 is kept abutted against a location on the tablet 31, electrostatic capacity coupling occurs between the X-electrode positioned in proximity to the location and the stylus pen 36, resulting in a voltage being output in the form of a coordinate detection signal from the stylus pen 36.
FIG. 11 is a graphical representation showing a voltage distribution due to electrostatic capacity coupling, wherein an abscissa axis indicates a location in an X-direction or a Y-direction and an ordinate axis indicates electrostatic capacity. As shown in FIG. 11, the electrostatic capacity is distributed in the form of a curved shape with respect to a location on the tablet 31 against which the stylus pen 36 is abutted. Therefore, during a period of scanning of an X-electrode (or Y-electrode) adjacent to a certain Y-electrode (or X-electrode), the stylus pen 36 generates a voltage along the curve shown in FIG. 11.
In view of the above, supposing that the coordinate detection signal shown in FIG. 11 is fed from the stylus pen 36 through the amplifier 37 to the peak detection circuit 38, for example, during scanning of a certain Y-electrode, the peak detection circuit 38 detects a peak position of the coordinate detection signal by means of a comparator or the like employing, for example, a voltage as a reference and feeds a peak position signal to the CPU 35 upon the detection.
Then, the CPU 35 discriminates the Y-electrode being scanned during a period corresponding to a timing at which the peak position signal is fed, resulting in the Y-electrode at the location at which the stylus pen 36 is abutted against the table 31 or the Y-coordinate being discriminated.
This is likewise applied to Y-coordinate detection. More particularly, during the X-coordinate detection period, a scan voltage is applied to the X-electrodes x.sub.1 to x.sub.m in turn for detection of an X-coordinate, to thereby obtain such a detection signal as shown in FIG. 11, resulting in a peak position signal of the voltage being fed to the CPU 35.
Thus, detection of a Y-coordinate as an input position is carried out during the Y-coordinate detection period and detection of an X-coordinate as an input position likewise takes place during the X-coordinate detection period, so that inputting of the X-coordinate and Y-coordinate by the stylus pen 36 is carried out.
In the conventional display-integrated tablet device constructed as described above, it is required to carry out both image display and coordinate detection by means of the same tablet, so that the one-image-plane display period is required to be divided into the actual display period and the X-coordinate detection period and Y-coordinate detection period, as shown in FIGS. 10(a) to 10(l).
Also, during the detection period, a pulse-like scan voltage of tens to hundreds of volts is applied to the X-electrodes and Y-electrodes in turn, so that the scan pulse is required to have a pulse width as long as several microseconds for every electrode. This causes a period of time required for detection during the one-image-plane display period or a period corresponding to display interruption to be considerably increased, so that the actual display period is reduced correspondingly.
Normally, in such display, the one-image-plane display period is defined to be about 1/60 to 1/70 second (about 16.7 to 14.2 ms). For example, supposing that sixty Y-electrodes and eighty X-electrodes are scanned at a pulse width of 5 .mu.s for detection in turn by means of a high speed driver, detection of the X-coordinate and Y-coordinate requires a period as long as (60.times.5)+(80.times.5)=700 .mu.s (0.7 ms), so that a period of time required for detection of the X-coordinate and Y-coordinate accounts for a considerable percentage of the one-image-plane display period.
Such a decrease in percentage for which the actual display period accounts of the one-image-plane display period causes an image displayed to be darkened.
Also, when the stylus pen 36 is used for not pointing but letter or character recognition, it is required that movement of the stylus pen 36 at a suitable speed on the tablet 31 for coordinate detection is carried out at least for every 1/120 second (about 8.3 ms) in view of detection accuracy. Thus, when coordinate detection during the one-image-plane display period takes place, for example, twice or more, the display period is decreased because a relationship between the pulse width and the number of electrodes scanned does not permit the coordinate detection period to be decreased, so that the displayed image may be further darkened to a degree sufficient not to be put to practical use.